In order to facilitate the power supply of electrical devices exchanging data with further equipment, mechanisms have been developed that allow for supplying the electrical devices with power via the same wired links which are used for the data exchange. In accordance with such mechanisms, power may be carried on the same conductors of the wired links as the data, or power may be carried on dedicated conductors in the same cable. Thus, it is not necessary to provide additional cabling for supplying power to the electrical devices.
One such mechanism is known as Power over Ethernet (PoE) and is described in the IEEE standard 802.3af-2003. The PoE mechanism allows for passing electrical power from a so called power sourcing equipment (PSE) to a powered device (PD) on the same Ethernet link that is also used for exchanging data between the PSE and the PD. Examples of powered devices which may be supplied with power by means of the PoE mechanism include classical network devices, such as IP phones, IP cameras, wireless access points and network routers. Moreover, solutions extending the PoE mechanism to other devices than such classical network devices have been suggested and developed. One related example includes the use of the PoE mechanism for powering and controlling lighting equipment connected to a lighting network via Ethernet connections.
Usually, powered devices which can be supplied with power via a data link have different power requirements particularly depending on the maximum power that such powered devices consume. In this regard, several classes of powered devices are defined in the aforementioned PoE mechanism, where each class corresponds to a certain current and power range. In order to provide an appropriate amount of power to the powered device, the apparatus has to determine the power requirements of the powered device. For this purpose, the apparatus usually reads a parameter specifying the power requirement from the powered device during a first period of a power cycle during which only a small voltage is provided to the powered device and which is also referred to a probing phase herein. In the context of the PoE mechanism, the parameter specifies the class of the powered device. On the basis of the parameter read from the powered device during the probing phase, the apparatus determines the appropriate configuration for the powered device. Then, it provides power to the powered device in accordance with the determined configuration in the normal mode of operation.
The aforementioned determination of the appropriate configuration for the powered device is made at the beginning of each power cycle, i.e. each time the apparatus switches from an inactive state in which no power is supplied to a powered device to an active state in which the apparatus supplies power to a powered device. Hereby, it is ensured that the apparatus always provides an appropriate amount of power to the connected powered device. In particular, it is ensured that an appropriate amount of power is supplied to a powered device which is newly connected to the apparatus before the start of the power cycle.